How to prevent or slowdown further rotting of pergola/arbor beam?

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Old 05-05-14, 04:01 PM
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How to prevent or slowdown further rotting of pergola/arbor beam?

I have a pergola in the backyard that has rot problem. I would appreciate any recommendation the group here can give. By the way, not sure if this piece of info would help, but I am in California with wet season between Oct to April and dry season without any rain between May to Oct.

The pergola in the backyard has this horizontal beam (10-12 ft long) spanning from the side of the house to a post. I am not sure what type of wood the builder used. The beam is a single piece of wood thatís about 8x8 inch in cross section and was painted with exterior latex paint matching to the color of the house. Unfortunately, it started to develop the rot on the top surface of the beam over the years and I didnít notice it until it was too late. The rot affects area with size about 2 feet long (along the long direction of the beam) by 8 inches (essentially the full width of the top beam surface). The rot ate away the materials and started to form a large dip on the top surface with various depths. At the deepest spot, close to 2 inch depths of woods rotted away. Making things worse, the dip gathers water when it rains and donít drain. The sitting water just get absorbed into the wood and make the issue worse and worse. The rest of the beam/pergola is in good shape.

What can I do to stop or slow down further rotting? Since the affected surface is on the top, it would hardly been seem by anyone, so I am less worried about the cosmetic aspect. I am more concerned about it gets progressively bad and eventually affecting the structural integrity of the beam itself. The beam is mostly just holding its own weight being supported on either end by the post and a metal ledge on the side of the house. I can see if the rot worsens much more significantly, it will become the weak point and could break.

I looked online and found a formula for borates (borax-boric acid mixtures) solution and applied it to the affected area after cleaning the area. I tried to patch up the affected area but it was a total failure. This is what I did: After applying the borates treatment and let it dry, I applied Elmerís rotted wood stabilizer and again let it dry/set. After that I tried to fill up the dip with Bondo over several sessions to build up the area. I thought it was all set when the affected areas were filled. Unfortunately, the Bondo, the rotted wood stabilizer, and the remaining wood donít stick to each other very strongly. Under the sun/elements, the cured Bondo/rotted wood stabilizer started to peel away on the edge at the junction from the wood. This lets the rain water to seep into gap. When I removed some of the Bondo, I could see the wood is wet/soft again and liquid/condensation gathers between the wood and the Bondo.

What can I do to stop or at least slow down the rot? The rain season is pretty much ended now and it wonít rain until Oct. Should I remove all the remaining Bondo (they are pretty strong and I may even need some tough tool to get it out) to have the affected wood fully exposed to air and open to good ventilation to dry? Or will the moisture gets sucked to the already exposed part and eventually dry out over the summer month?

More importantly, what can I do to stop water getting into the dip and accumulate in there and being absorbed by the wood? Is Bondo the right choice for this? Did I apply the wood stabilizer and Bondo incorrectly? Is building a metal flashing to cover up the affected area an option? How can I seal the gap between metal flashing and the wood beam? I can imagine bending down the metal sheet on either side of beam so liquid just run down the vertical surface, but what about the other two sides of the metal sheet that will be along the length of the beam? I clearly canít cover the entire length of the beam, so there will be a gap where the metal sheet meets the top surface of the wood. Can I use silicone caulk to seal it? Will any moisture gather on the underneath of the metal sheet and continue to cause problem?

Any suggestion is appreciated. Thanks.
 
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Old 05-06-14, 04:23 AM
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Welcome to the forums!

Whenever wood is that far gone it's best to bite the bullet and replace the affected boards.
When I paint/stain a pergola or trellis I like to apply an extra coat to the top, that area gets the most exposure to the elements and the coating will fail there first.
 
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Old 05-06-14, 12:52 PM
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If you want to save your beam, and it is not in any way "structural" (i.e., doesn't support other parts of structure, and therefore depends on full dimensional integrity), AND the rotted parts have not resulted in any measurable sag in the beam, it is possible to cut out the rot and fashion a "dutchman" of like material to fill the void. There really is no way at this point to "slow down the rot."

You'll need some tools and a little skill with them to neatly remove all rot and create a right angled void in the beam. Cut some material to that dimension, secure with screws and an outdoor rated adhesive and then paint. Insure your dutchman has the adhesive glue ooze to the surface at all joints so there is no future path for water.

As far as paint goes, it sounds as if the paint has failed on the top, so the entire beam should be repainted. I would sand at least the top with a very aggressive paper and if possible (you being in CA), coat the top with an oil based primer before applying two coats of water based paint.
 
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Old 05-06-14, 05:17 PM
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Thanks for the suggestions

Thanks for the suggestions. I will start off with the suggested repainting of the rest of the pergola right away while doing more research on how to put in the suggested "dutchman" fix.

Sounds like the affected areas need to be removed (and may be well beyond) to reach true "healthy" wood to get this to work? Does it sound like I need to cut off 3 inch deep of wood from that area for the full width of the beam that span 2 feet (along the long side of the beam) to form a big "notch" the size of 3 inch (depth) x 8 inch (width) x 32 inch (length) ?

What kind of tool does one need to cut off the top portion completely? (Sorry, I am definitely a novice in this).

Thanks again!
 
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Old 05-07-14, 04:31 AM
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For a dutchman repair to be successful you need to remove the rot and get down to solid wood. You also want the cut to be even/level. Probably the easiest way to make a straight cut would be to use a skil saw, I'm not sure how thick the wood is but if the blade won't make it all the way thru the wood you could cut it from both sides. Tacking up a 1x as a guide would help you keep the cut straight. You'll want to make sure you use a good exterior glue along with nails/screws to hold the 2 pieces of wood together..

IMO a dutchman would be more work than replacing the wood. You also run the risk of moisture getting trapped between the 2 pieces of wood which could start the rot process all over But I'm not there to inspect it and see just what all is involved to do the job

If you have access to a table saw, cutting a bevel on the top of the wood will give it a leg up on shedding rain water
 
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Old 05-08-14, 01:02 AM
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Thanks for the insights. Time to get more tools.
 
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Old 05-08-14, 10:43 PM
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I am having the same issue
 
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Old 05-09-14, 04:10 PM
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I start to feel that this may be beyond my skill level. Which type of contractors I should hire if I decide to go that route?

Thanks
 
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Old 05-09-14, 04:13 PM
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Most any carpenter and many handymen can do the job. Be sure to check their references first!
 
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Old 05-09-14, 05:27 PM
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Notching a beam with smooth cuts is not difficult. And hiring someone to do it for you will easily cost $200 or more. Make that $300 or more, since you're in California. For less than half that amount, you could easily buy a new member and completely replace the rotted one. Doing so would also enable you to check the condition of the top of the support column, too, since end-grain areas are notoriously more susceptible to rotting.
 
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Old 05-12-14, 06:58 PM
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Is it me or does horizontal wood rot fast? From fencing, shooting range, to our arbor, everything horizontal is going to the dogs. My guess is horizontal grain holds moisture?!?

Couple of questions for those in the know. Could you use treated lumber instead and not paint? Can you nail/butt up treated wood for extended lengths without worrying about rot/warping, etc.?
 
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Old 05-13-14, 04:51 AM
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Rain water will set on horizontal wood until the sun evaporates it. That's why the stain on a deck won't last as long as the stain on siding. Using PT wood helps, there are also several species of wood that have natural tendencies to withstand the elements; redwood, cedar and cypress being the most common. IMO stain/paint will make any wood last longer, including PT .... but I am a painter

Can you nail/butt up treated wood for extended lengths without worrying about rot/warping, etc.?
It depends on the application, dimensions of the wood and the span. I have a fence behind my house that has PT 1x6 decking for rails with the posts set every 8' and there is no warping or sagging.
 
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